1. Field of the Invention
The invention relates to a wideband low noise amplifier, and more particularly to an ultra-wideband (UWB) low noise amplifier.
2. Description of the Related Art
Recently, wideband systems with high frequency transmission capabilities have become more and more popular. For example, ultra-wideband (UWB) system using 3.1 GHz to 10.6 GHz transmission bands offering faster speed and wireless transmission capabilities. Along with development of wideband technology, the bandwidth of the elements adopted in the wideband systems must also be extended. For example, a low noise amplifier (LNA) disposed between an antenna and pre-select filter in the UWB system requires a 50Ω input resistance and 3.1 GHz to 10.6 GHz bandwidth design.
FIG. 1 shows a conventional low noise amplifier 10, which is a type of distributed amplifier (DA). Because the frequency response of a DA can be extended to a direct current (DC) part and there is a good match between the input-output resistances, the distributed low noise amplifier 10 is now widely used in wideband systems. However, the distributed low noise amplifier 10 requires a large chip area and high power consumption. FIG. 2 shows another conventional low noise amplifier 20, which is a type of cascode CMOS LNA. Cascode CMOS LNA 20 includes a bandpass filter in the input end for providing a good wideband match of the input resistance and wideband frequency response. However, since the bandpass filter in the input end requires lots of inductors and capacitors, the cascode CMOS LNA 20 has large noise figure (NF) and requires a large chip area when implemented. To achieve a wideband match with low noise dissipation and smaller chip area, common gate input topology has been developed. FIG. 3 is another conventional low noise amplifier 30, which is a common gate LNA. However, the gain of the common gate LNA 30 is small and NF of the common gate LNA 30 is large when compared to a common source amplifier.
Thus, an improved wideband low noise amplifier with low power consumption, wideband resistance match and a small chip area for a UWB system is required.